The present disclosure relates to an electrostatic charge image developing toner and a method for producing an electrostatic charge image developing toner.
In the technical field of image formation by electrophotography, an electrostatic charge image developing toner is fixed to a recording medium such as paper by heat and pressure applied using a fixing roller. For saving energy for the fixing and downsizing apparatuses, an electrostatic charge image developing toner has been desired to have improved low-temperature fixability such as to be fixable at a temperature as low as possible. However, an electrostatic charge image developing toner having improved low-temperature fixability contains a binder resin having a low softening point (Tm) and a low glass transition point (Tg), and a releasing agent having a low softening point (Tm). Accordingly, toner particles contained in the electrostatic charge image developing toner tend to unfavorably aggregate when the electrostatic charge image developing toner is stored at high temperatures. An electrostatic charge image developing toner containing aggregated toner particles is more likely to have a reduced charge compared to an electrostatic charge image developing toner containing non-aggregated toner particles. The aggregated toner particles therefore tend to undesirably contribute to development. Consequently, a resulting image may have a defect.
In order to produce an electrostatic charge image developing toner having excellent low-temperature fixability, therefore, it has been desired to improve the preservability of toner at high temperatures and to reduce blocking of toner particles. To this end, a toner containing toner particles having a core-shell structure has been used. Toner particles of such an electrostatic charge image developing toner have a core-shell structure in which toner cores contain a binder resin having a low-melting point, and a surface of each toner core is coated with a shell layer containing a thermosetting resin. The shell layers have a higher glass transition point (Tg) than the binder resin contained in the toner cores.
As the electrostatic charge image developing toner having the core-shell structure, for example, an electrostatic charge image developing toner has been proposed in which the surface of each toner core has a shell layer containing a thermosetting resin. The toner cores have a softening point (Tm) of 40° C. or higher and 150° C. or lower.
In another example of the electrostatic charge image developing toner, a thermoplastic resin is used for the shell layers. Specifically, films of the shell layers are formed by melting the thermoplastic resin. In such an electrostatic charge image developing toner, the shell layer coating the surface of each toner core has a film thickness of 50 nm or more and 200 nm or less.